Erbium: the essentials

Pure erbium metal is soft and malleable and has a bright, silvery, metallic lustre. As with other rare-earth metals, its properties depend to a certain extent on impurities present. The metal is fairly stable in air and does not oxidise as rapidly as some of the other rare-earth metals.

This sample is from The Elements Collection, an attractive and safely packaged collection of the 92 naturally occurring elements that is available for sale.

Erbium: historical information

Erbium was discovered by Carl G. Mosander in 1842 at Sweden. Origin of name: named after the village of "Ytterby" near Vaxholm in Sweden.

In 1842 Gustav Mosander separated "yttria", found in the mineral gadolinite, into three fractions which he called yttria, erbia, and terbia. The names erbia and terbia became confused in this early period. After 1860, Mosander's terbia was known as erbia, and after 1877, the earlier known erbia became terbia. The erbia of this period was later shown to consist of five oxides, now known as erbia, scandia, holmia, thulia and ytterbia. Klemm and Bommer first produced reasonably pure erbium metal in 1934 by reducing the anhydrous chloride with potassium vapour.

Erbium has no biological role but is said to stimulate the metabolism.

Erbium is never found in nature as the free element. Erbium is found in the ores monazite sand [(Ce, La, etc.)PO4] and bastn°site [(Ce, La, etc.)(CO3)F], ores containing small amounts of all the rare earth metals. It is difficult to separate from other rare earth elements.

Isolation

Isolation: erbium metal is available commercially so it is not normally necessary to make it in the laboratory, which is just as well as it is difficult to isolate as the pure metal. This is largely because of the way it is found in nature. The lanthanoids are found in nature in a number of minerals. The most important are xenotime, monazite, and bastnaesite. The first two are orthophosphate minerals LnPO4 (Ln deonotes a mixture of all the lanthanoids except promethium which is vanishingly rare) and the third is a fluoride carbonate LnCO3F. Lanthanoids with even atomic numbers are more common. The most comon lanthanoids in these minerals are, in order, cerium, lanthanum, neodymium, and praseodymium. Monazite also contains thorium and ytrrium which makes handling difficult since thorium and its decomposition products are radioactive.

For many purposes it is not particularly necessary to separate the metals, but if separation into individual metals is required, the process is complex. Initially, the metals are extracted as salts from the ores by extraction with sulphuric acid (H2SO4), hydrochloric acid (HCl), and sodium hydroxide (NaOH). Modern purification techniques for these lanthanoid salt mixtures are ingenious and involve selective complexation techniques, solvent extractions, and ion exchange chromatography.

Pure erbium is available through the reduction of ErF3 with calcium metal.

2ErF3 + 3Ca → 2Er + 3CaF2

This would work for the other calcium halides as well but the product CaF2 is easier to handle under the reaction conditions (heat to 50°C above the melting point of the element in an argon atmosphere). Excess calcium is removed from the reaction mixture under vacuum.

Erbium has six stable isotopes but only Er-168 appears to have a well established application. Er-168 is used for the production of Er-169 which is used in form of citrate for the treatment of rheumatoid arthritis.